Electric power steering apparatus

ABSTRACT

An electric power steering apparatus includes a steering shaft having its upper end to which a steering wheel is fitted, a steering column rotatably supporting the steering shaft, tilting about a pivot as a fulcrum and moving telescopically together the steering shaft in axis-directions, an electric assist motor unit attached to the steering column and serving for a steering assist of the steering wheel, and a tilt/telescopic adjustment means for fixing the steering column in a predetermined angular position and fixing the steering column in a predetermined axis-directional position, wherein the pivot is disposed between the electric motor unit and the tilt/telescopic adjustment means.

TECHNICAL FIELD

The present invention relates generally to an electric power steeringapparatus, and more particularly to a technology contrived for attainingsmooth operations of a telescopic adjustment and of a tilt adjustment,and so on.

BACKGROUND ARTS

A steering system for an automobile widely adopts a so-called powersteering apparatus for having a steering assist performed by use of anexternal power source.

Generally, the power source for the power steering apparatus hashitherto involved the use of a vane type hydraulic pump that is drivenby an engine in many cases. This type of power steering apparatus has,however, a large drive loss of the engine as the hydraulic pump isdriven without interruption (the drive loss is on the order of severalhp (horsepower) to several tens of hp when at the maximum load). It istherefore difficult to adopt this power steering apparatus formini-sized motor vehicles, etc. having a small displacement, and atraveling fuel efficiency of even an automobile having a comparativelylarge displacement inevitably decreases down to an unignorable degree.

Such being the case, over the recent years, an emphasis for solvingthese problems has been placed on an electric power steering (which willhereinafter be abbreviated to EPS) apparatus employing an electric motoras a power source. The EPS exhibits features, wherein the EPS uses anon-vehicle battery as a power source of the electric motor and thereforehas no direct drive loss of the engine, a decline of traveling fuelefficiency (which is a drive loss of the engine related to analternator) can be restrained as the electric motor is started up onlywhen in the steering assist, and in addition execution of the electroniccontrol can be highly facilitated. Note that the EPS is classified intoa column assist type, a rack assist type, etc., depending on where theelectric motor is installed, however, at the present the most-widespreadtype is the column assist type having merits in terms of a manufacturingcost, a space, and so on. It should be noted that a general version ofthe column assist type electric power steering apparatuses is that thesteering shaft, as disclosed in Japanese Patent Application Laid-OpenNo. 2000-855596, gets collapsed upon receiving a predetermined impactload in order to relieve a secondary collision of an occupant (driver)with the steering wheel when an automotive vehicle encounters the(primary) collision.

On the other hand, the steering apparatus of the automobile is used(steered) by a majority of unspecified drivers, and it is thereforedesirable that a position of the steering wheel can be adjustedcorresponding to an individual physique, a driving posture, etc. Formeeting such a request, there increases the number of trucks or lorriesand the like without being limited to the passenger cars, which adopt atilt adjustment mechanism and a telescopic adjustment mechanism. Thetilt adjustment mechanism is a mechanism for adjusting a position of thesteering wheel in up-and-down directions. The tilt adjustment mechanismis constructed of a tilt pivot for supporting the steering column in aswingable manner, a tilt lever for fixing the steering column in adesired position (at a desired tilt angle), and so on. Further, thetelescopic adjustment mechanism is a mechanism for adjusting theposition of the steering wheel in the front-and-rear directions (in theaxis-directions of the steering shaft). The telescope adjustmentmechanism is constructed of a telescopic portion of a double-pipe typeor the like that serves for lengthening or shortening the steeringshaft, a telescopic lever for fixing the steering shaft in a desiredposition (with a desired lengthening or shortening quantity), and soforth.

The column assist type electric power steering apparatus provided withboth of the tilt adjustment mechanism and the telescopic adjustmentmechanism, is exemplified by what is disclosed in Japanese PatentApplication Laid-Open Nos. 11-301492 and 2000-211533, etc. Thoseelectric power steering apparatuses, however, present a problem, whereinsmooth operations of the telescopic adjustment and the tilt adjustmentwere not attained due to such a layout that the tilt pivot is disposedat a lower end of the steering column.

For example, as illustrated in FIG. 5, a comparatively heavy electricassist mechanism 17 structured of an electric motor, a speed reducinggear, etc. is attached to a steering column 1. When making thetilt/telescopic adjustments, however, a weight of this electric assistmechanism 17 is applied to between the tilt pivot 31 and the steeringwheel, and consequently a large bending stress acts on a fitting slideportion 71 between an upper column 13 and a lower column equivalentmember 15 that configure a telescopic mechanism. As a result, thislarger bending stress and incapacity of increasing a length L of thefitting slide portion 71 because of an existence of the electric assistmechanism 17, are combined into an occurrence of torsional blockingbetween the upper column 13 and the lower column equivalent member 15,with the result that the telescopic adjustment operation can not besmoothly performed. This unsmoothed operation is conspicuous because ofa single-hand telescopic operation conducted in a way that releases alever with one hand while grasping the steering while with the otherhand.

In the case of increasing the length L of the fitting slide portion 71in order to improve this problem, a problem arises, wherein a collapsingstroke of the steering upper shaft 9 decreases as well as a telescopicstroke S, a degree of freedom for the telescopic adjustment decreases,and at the same time safety of the occupant (driver) against thesecondary collision is hindered. Moreover, when in the tiltingoperation, a total weight of the steering column 1 including theelectric assist mechanism 17 acts on the tilt pivot 31 as a fulcrum, andhence a smooth tilting operation still remained unperformable even byuse of a tilt assist spring 65 having large spring force.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, which was devised under suchcircumstances, to provide an electric power steering apparatus contrivedfor attaining smooth telescoping and tilting operations.

To accomplish the above object, an electric power steering apparatusaccording to the present invention, includes a steering shaft having itsupper end to which a steering wheel is fitted, a steering columnrotatably supporting the steering shaft, tilting about a tilt pivot as afulcrum and effecting a telescopic movement together with the steeringshaft in axis-directions, an electric assist motor unit attached to thesteering column and serving for a steering assist of the steering wheel,and a tilt/telescopic adjustment means for fixing the steering column ina predetermined angular position and fixing the steering column in apredetermined axis-directional position, wherein the tilt pivot isdisposed between the electric motor unit and the tilt/telescopicadjustment means.

According to the present invention, there decrease both of a bendingstress acting on a telescopic fitting slide portion and a load acting onthe steering column upwardly of the tilt pivot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing a vehicle compartment sidedstructure of a steering apparatus according to the present invention;

FIG. 2 is a side view of a steering column according to a firstembodiment of the present invention;

FIG. 3 is a sectional view taken along the line A—A in FIG. 2;

FIG. 4 is a sectional view taken along the line B—B in FIG. 2; and

FIG. 5 is a side view showing one example of a conventional steeringcolumn.

EMBODIMENT OF THE INVENTION

An embodiment of the present invention will hereinafter be describedwith reference to the drawings.

FIG. 1 is a side view showing a vehicle compartment sided portion of anelectric power steering apparatus according to a first embodiment of thepresent invention. FIG. 2 is a side view of a steering column. Asillustrated in FIGS. 1 and 2, a steering column 1 is supported on across member 7 defined as a vehicle body structural member throughrespective horizontal portions 3 a and 5 a of an upper bracket 3 and alower bracket 5. The steering column 1 is constructed mainly of theupper column 13 for rotatably holding, via a bearing 11, an upper shaft9 of a steering shaft having a telescopic adjustment function and acollapsing function for absorbing energy, an outer jacket 15 in whichthe upper column 13 is slidably fitted, and an electric assist mechanism17 integrally provided at a lower side end of the outer jacket 15.

The electric assist mechanism 17 is constructed of an electric motorunit 21, a speed reducing gear housing 23 that accommodates a speedreducing gear train for transferring rotational driving force given fromthe electric motor unit 21 to an output shaft 25 provided at a front endof the steering shaft, a torque sensor (unillustrated) for a steeringtorque applied to the steering wheel 41, and so forth. In the case ofthe present embodiment, the outer jacket 15 and the speed reducing gearhousing 23 are formed as an integrally molded product formed of analuminum alloy as a material. The outer jacket 15 and the gear housing23 may also be formed separately and then assembled into one united bodyby pressfitting and the like. A lower end of the electric motor unit 21is fixed to a rearsided upper surface of the speed reducing gear housing23. A pivot bracket 33 is integrally formed on an upper portion of theouter jacket 15 behind the electric motor unit 21 and the speed reducinggear housing 23. The pivot bracket 33, which is a countertype of thelower bracket 5, is connected to the lower bracket 5 in such a way thata pivot pin 31 a is inserted through through-holes formed in verticalportions 5 b of the lower bracket 5 and fastened by a nut 31 b viabushes 100. In FIG. 1, the numeral 35 designates a steering intermediateshaft connected to a front end of the output shaft 25 through auniversal joint 37. The intermediate shaft 35 is defined as a telescopicshaft and connected to a rack-and-pinion mechanism of a steeringmechanism that is provided at a lower part of the car body.

The steering wheel 41 is fitted to a rear end of the steering uppershaft 9. When a driver rotates the steering wheel 41, rotational forcethereof is, after being increased with an assistance of the electricassist mechanism 17, transferred to the steering intermediate shaft 35via the output shaft 25 and further to the aforementionedrack-and-pinion mechanism through an unillustrated lower-sided universaljoint.

As shown in FIG. 3 (which is a sectional view taken along the line A—Ain FIG. 2), a couple of right-and-left bosses 43, 45 abutting oninternal wall surfaces of vertically extending portions 3 b, 3 b of theupper bracket 3, are integrally formed so as to protrude from the lowerportion of the rear end of the outer jacket 15. Then, a slit 47 isformed extending in the axial direction at the center of the lowerportion of the outer jacket 15. Further, through-holes 48, 49 coaxialwith each other are formed in the two bosses 43, 45. An adjustment bolt53 as a component of a tilt/telescopic adjustment mechanism 51 isinserted through these through-holes 48, 49. A guide bolt 55 is providedinwards in a radial direction on an upper portion of the outer jacket15, and a front side end of the guide bolt 55 engages with a groove 13 aformed extending in the axial direction in a corresponding position ofan upper portion of the upper column 13, whereby the guide bolt 55guides the upper column 13 when in a telescopic operation and serves asa stopper when making a telescopic adjustment.

The tilt/telescopic adjustment mechanism 51 includes, in addition to theaforementioned adjustment bolt 53, an adjusting nut 57 screwed onto theadjustment bolt 53 and an operation lever 61 fastened to the adjustmentnut 57 by a bolt 59. In the case of the present embodiment, a truncatedcone portion of the adjustment nut 57 is taperfitted in a truncated conerecessed portion of the operation lever 61. When rotating the operationlever 61 counterclockwise, the upper bracket 3 is fastened by theadjustment nut 57 and the adjustment bolt 53. When rotating theoperation lever 61 clockwise, the upper bracket 3 is released from beingfastened. In FIG. 3, the numeral 63 represents elongate holes formed inthe upper bracket 3, and the adjustment bolt 53 moves along within thiselongate hole 63 when in a tilting operation. Further, members indicatedby the numeral 65 in FIG. 3 are tilt assist springs stretched betweenthe upper bracket 3 and the outer jacket 15. When the upper bracket 3 isreleased from being fastened through the operation of the operationlever 61, elastic force of the tilt assist springs 65 prevents an abruptmovement of the steering column.

An operation of the present embodiment will hereinafter be described.

If the steering wheel 41 gets improper in its position due to areplacement of the driver, etc., according to the electric powersteering apparatus in the first embodiment, the driver at first rotatesthe operation lever 61 clockwise, thereby slackening the adjustment nut57 from the adjustment bolt 53. Hereat, there dissipates an axial forceof the adjustment bolt 53, which has been acting on the upper bracket 3and on the bosses 43, 45 of the outer jacket 15, with the result thatthe steering column 1 becomes swingable by a predetermined quantityabout the pivot pin 31 as a fulcrum and at the same time the uppercolumn 13 gets slidable by a predetermined quantity on the outer jacket15. This being done, the driver can adjust the steering wheel 41 in adesired position by tilting or telescopically moving the steering column1.

Upon finishing the positional adjustment of the steering wheel 41, thedriver rotates the operation lever 61 counterclockwise, therebyfastening the adjustment nut 57 against the adjustment bolt 53. Then, apredetermined axial force occurs upon the adjustment bolt 53, wherebythe upper bracket 3 is press-fitted to the bosses 43, 45, andsimultaneously the upper column 13 is secured as a diameter of the outerjacket 15 is reduced. The tilt and telescopic adjustments of thesteering column 1 are thereby completed, and the steering wheel 41 isfixed in the desired position.

According to the present embodiment, since the pivot pin 31 for the tiltadjustment is positioned behind the electric motor unit 21, a centroidalposition of the electric motor is (sic) and, a bending stress caused bya weight of the electric assist mechanism 17 does not act on a fittingslide portion 71 between the upper column 13 and the outer jacket 15. Asa result, torsional blocking is hard to occur between the upper column13 and the outer jacket 15, whereby a smooth telescoping motion can beattained. Further, a length L of the fitting slide portion 71 can becomparatively made short for the same reason. It is therefore possibleto ensure both of a sufficient telescopic stroke S of the upper column13 and a sufficient collapsing stroke of the steering upper shaft 9,whereby a degree of freedom for the positional adjustment of thesteering wheel and the safety of an occupant (driver) against asecondary collision are improved.

On the other hand, according to the present embodiment, the electricmotor unit 21 is positioned anterior to the pivot pin 31, while thetilt/telescopic adjustment means is positioned posterior to the pivotpin 31, thereby improving a weight balance between the anteriority andthe posteriority to the pivot pin 31. This improvement does not requiregreat spring force of the tilt assist spring 65 and enables the tiltingoperation to be conducted easily and smoothly.

The discussion on the specific embodiment is finished so far, however,the mode of the present invention is not limited to the embodimentdescribed above. For example, the tilt pivot 31 is provided upwardly ofthe steering shaft in the embodiment discussed above and may also beprovided downwardly. Further, the tilting direction and telescopicdirection of the steering column are fixed by use of the singleoperation lever and may also be adjusted by dedicated pieces ofoperation levers. Moreover, the specific constructions, etc. of theelectric assist mechanism enumerated first, the tilt mechanism and thetelescopic mechanism can be properly changed if within the scope thatdoes not deviate the gist of the present invention.

As discussed above, in the electric power steering apparatus accordingto the present invention, there are decreases in the bending stressacting on the telescopic fitting slide portion and in the load acting onthe upper portion of the tilt adjusting pivot, thereby enabling thetelescopic adjustment operation and the tilt adjustment operation to beperformed smoothly. In addition, the length of the fitting slide portionbetween the upper column and the outer jacket can be made comparativelyshort, and it is therefore feasible to ensure the sufficient telescopicstroke of the upper column and the sufficient collapsing stroke of theupper shaft and to improve both the degree of freedom for the positionaladjustment of the steering wheel and the safety of the occupant (driver)against the secondary collision.

1. An electric power steering apparatus, comprising: a steering shafthaving an upper end to which a steering wheel is fitted; a steeringcolumn rotatably supporting said steering shaft, tilting about a pivotas a fulcrum and moving telescopical together with said steering shaftin axial directions; an electric assist motor unit attached to saidsteering column and serving for a steering assist of said steeringwheel; and tilt/telescopic adjustment means for fixing said steeringcolumn in a tilt-adjusted angular position and fixing said steeringcolumn in a telescopically adjusted axial-directional position, whereinsaid pivot is disposed between said electric motor unit and saidtilt/telescopic adjustment means, and above said steering shaft.
 2. Anelectric power steering apparatus, comprising: a steering shaft havingan upper end to which a steering wheel is fitted; a steering columnrotatably supporting said steering shaft, said steering column beingtiltable about a pivot and movable telescopically together with saidsteering shaft in axial directions; an electric assist motor unitattached to said steering column and providing a steering assist forsaid steering wheel; and a tilt/telescopic adjustment mechanism operableto adjustably fix tilt and telescopic positions of said steering column,wherein said pivot is disposed between said electric motor unit and saidtilt/telescopic adjustment mechanism, and above said steering shaft.